On Fri, Mar 28, 2014 at 10:44:11PM +0100, Artur Skawina wrote:
> On 03/28/14 20:00, H. S. Teoh wrote:
> > Today I ran into an interesting situation where I have a function f
> > that needs to return ranges of different types (but identical
> > element types):
> >
> > auto f(A...)(A args) {
> > ...
> > if (someCondition)
> > return cartesianProduct(x, y)
> > .joiner;
> > else
> > return cartesianProduct(x, y)
> > .joiner
> > .filter!someFilter;
> > }
> >
> > This obviously can't compile, because the return types are not the
> > same. (Note that someCondition is only known at runtime.) But
> > abstractly speaking, it *should* work, because the element type of
> > the returned range is identical.
> >
> > So how would I implement something like this?
>
> eg
> auto f(A...)(A args) {
> ...
> return cartesianProduct(x, y)
> .joiner
> .filter!(a=>somecondition?true:somefilter(a));
> }
[...]
It's not that simple, though. I guess I gave a bad example. In the
actual code, someCondition decides whether or not a cartesian product is
even used. So the return range needs to somehow switch between a
cartesianProduct filtered by some filters, vs. an alternative algorithm
filtered by some other filters.
T
--
Famous last words: I *think* this will work...
